No family members have been allowed to visit Kamal Foroughi during his time in jail.
Photograph: Supplied

The family of a 76-year-old British-Iranian businessman imprisoned in Iran for more than four years has called on David Cameron to do more to secure his release in the wake of Tehran’s recent prisoner swap with the US.

Kamal Foroughi, who has been described by his family as one of the “oldest and loneliest prisoners in Iran”, was working in Tehran as a consultant for the Malaysian national oil and gas company Petronas before his arrest in May 2011. He was held at the notorious Evin prison and eventually sentenced in 2013 to a total of eight years’ imprisonment, which he is still serving.

His ordeal only came to light in October when his son, Kamran Foroughi, spoke to the Guardian about the nightmare his family have gone through.

On Monday Kamran said he expected the British government to step up efforts to free his father. “Today is day 1,720 of my dad’s detention,” he told the Guardian. “We are very worried about his health. He had a medical on Tuesday 17 November, but we still haven’t heard any news about what tests were done or the outcome of those tests.”

According to Kamran, no family members have been able to visit his father in jail in the past four years and he is not allowed any visitors apart from his lawyer. “My dad had a meeting with his lawyer Saturday morning, and reported back to us that he was feeling hopeful about the near future,” Kamran said, citing the news that Iran had swapped five Americans, of which four were dual nationals, in exchange for seven Iranians jailed in the US on charges of violating sanctions.

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“I am really pleased that the US prisoners were released and returned to their families, which must be of great relief,” Kamran said. “I was in touch with the Foreign Office on Saturday afternoon shortly after the US prisoners were released, which was helpful. Of course, until grandpa Kamal is released and back here with his family, I will always want the UK government to do more.”

Foroughi’s consultancy role at Petronas included arranging and participating in meetings with senior Iranian oil and gas officials and facilitating scholarships for Iranian students on a government bursary to study in Malaysia.

It is not clear on what evidence Iran convicted him on spying charges. Foroughi holds both British and Iranian citizenships. Iran’s intelligence authorities view dual nationals with deep suspicion and have arrested a number of them in recent years, including the Iranian-American journalist Jason Rezaian, one of the four involved in the prisoner swap.

According to Hadi Ghaemi, of the International Campaign for Human Rights in Iran, other dual and foreign nationals who remain in jail in the country include Siamak Namazi, an Iranian-American arrested in September 2015, and the Lebanese national Nazar Zaka, who lived in the US and was arrested while attending a conference in Tehran in the same month.

In 2013, an upper court sentenced Foroughi to seven years in jail for espionage and an extra year for possessing alcohol at home. Kamran has previously suggested his father’s friendship with a former British ambassador in Tehran might have caused him trouble. Iran has not publicly commented on his detention and he has had little access to his lawyer.

An online petition calling on Iran to release Foroughi has gained nearly 80,000 signatures on Change.org.

Amnesty International has previously said: “Kamal Foroughi suffers from different medical conditions and Amnesty International understands that, prior to his arrest, his doctors had said that he needed specialised medical tests and checkups, including screening for cancer. He has been transferred to a hospital outside prison several times since December 2014, but has not received the care he needs because no specialists have been available.”

A Foreign Office spokesman said: “We are very concerned for Mr Foroughi’s health and have raised this with the Iranian authorities on repeated occasions, urging them to provide regular medical assistance and access to a lawyer. We have been in regular contact with his family since we were first made aware of his situation in May 2013 and Middle East minister Tobias Ellwood has met with his son to discuss the case directly. However, Iran does not recognise dual nationality and as such is not granting us consular access.

“The foreign secretary has personally raised this case with Iran’s president [Hassan] Rouhani in Tehran and also with their foreign minister [Mohammad Javad] Zarif. We will continue to raise it with the Iranian government at every opportunity, seeking Mr Foroughi’s release on medical grounds.”